Examine source code of AudioSpeedController_v2

{
  "manifest_version": 2,
  "name": "AudioSpeedController",
  "version": "0.1",
  "content_scripts": [
    {
      "matches": [
        "https://web.whatsapp.com/"
      ],
      "css": [
        "style.css"
      ],
      "js": [
        "extension.js"
      ]
    }
  ],
  "icons": {
    "16": "./icons/icon16.png",
    "48": "./icons/icon48.png",
    "128": "./icons/icon128.png"
  }
}